Radiocarbon ages of insects and plants frozen in the No. 31 Glacier, Suntar-Khayata Range, eastern Siberia

The shrinkage of Arctic glaciers by recent global warming has become a major concern. However, the variation of glaciers in the Suntar-Khayata Range, eastern Siberia, is not well understood due to a lack of observations. To ascertain the current conditions and forecast the future variation of the glaciers, glacier observations in this region have been carried out since 2011 as part of the research project "The role of Arctic cryosphere in global change" within the framework of the Green Network of Excellence (GRENE) Program funded by the Ministry of Education, Culture, Sports, Science and Technology, Japan.

Among the glaciers in this region, the No. 31 Glacier has been the most extensively observed and is considered to be a representative case [2]. The glacier is situated in the northern part of the Suntar-Khayata Range and is located approximately 510 km west of Yakutsk, the capital of the Sakha Republic (Fig. 1). According to Ananicheva et al. [2] and Galanin et al. [3], the first findings detailing the presence of glaciers were reported at the end of the nineteenth century, and the systematic study of glaciation on the No. 31 Glacier began in only the late 1950s as part of research during the International Geophysical Year (IGY) in 1957–1959. In 1970, glacier observations were again carried out under the project "Compilation of the Catalogue of the USSR glaciers". After that, glaciation in this region was not studied again until the beginning of the 2000s. These previous studies have revealed that as of 2001, the No. 31 Glacier has shrunk by as much as 350 m since the Little Ice Age, with more than 150 m of this shrinkage occurring between 1947 and 2001 [2]. In the last decade, the glaciers in this region have been receiving renewed attention due to their recent sharp decline. In addition, data for making a comparison between the present and the IGY period are expected to enable analysis of changes of the glaciers (e.g. [2], [5], [13], [16], [21]).

In the 2012–14 observations, dead insects such as moths (Lasiocampidae), longhorn beetles (Monochamus sutor), and long-legged flies (Dolichopodidae) could be easily found on the surfaces of the No. 31 Glacier and its neighboring glaciers (Fig. 2a–c), along with some living insects. Although certain insects, such as those belonging to the chironomid genus Diamesa, are known to spend their entire life cycle in glacial snow and ice [6], no previous studies have reported such behavior for the insects observed in the present study. Dolichopodid flies in both the larval and adult stages are predators and can be found in all wet biotopes. As larvae are mostly aquatic or semi-aquatic and adults usually do not usually fly very far from their breeding site [4], the insects could have been brought to the glaciers by wind. In the 2013 observation, dead insects thought to be dolichopodid flies as well as plant fragments of unknown species were collected from subsurface glacier ice at several points on the No. 31 Glacier. The aim of this study was to estimate the age of the glacier ice by radiocarbon dating of the organisms preserved within it.

To date, only a few reports have estimated the age of glacier ice by radiocarbon dating, which is possible only when insects and plant fragments are discovered serendipitously in ice samples. Thompson et al. [17] found intact insects, insect fragments, and Polylepis bark fragments within the Sajama ice core drilled in Bolivia. Those organic materials had sufficient mass for radiocarbon dating, which was performed at an accelerator mass spectrometry (AMS) facility to estimate the age of the ice core layers.